feat: 🎸 trim blank lines, improve performance

Author: streamich

src/__tests__/printTree.spec.ts

@@ -43,3 +43,67 @@ test('renders two levels of nodes, with double tree line', () => {
    └─ baz`,
   );
 });
+
+test('family tree example', () => {
+  // prettier-ignore
+  const str = 'Me' + printTree('', [
+    (tab) => `Father` + printTree(tab, [
+      (tab) => `Grandfather` + printTree(tab, [
+        () => `Great-grandfather`,
+        () => `Great-grandmother`,
+      ]),
+      () => `Grandmother`,
+    ]),
+    (tab) => `Mother` + printTree(tab, [
+      () => `Grandfather`,
+      () => `Grandmother`,
+    ]),
+  ]);
+
+  expect('\n' + str).toBe(
+    `
+Me
+├─ Father
+│  ├─ Grandfather
+│  │  ├─ Great-grandfather
+│  │  └─ Great-grandmother
+│  └─ Grandmother
+└─ Mother
+   ├─ Grandfather
+   └─ Grandmother`,
+  );
+});
+
+test('can add a blank line', () => {
+  // prettier-ignore
+  const str = 'start' + printTree('', [
+    (tab) => 'line 1',
+    () => '',
+    (tab) => 'line 2',
+  ]);
+
+  expect('\n' + str).toBe(
+    `
+start
+├─ line 1
+│
+└─ line 2`);
+});
+
+test('can produce wide tabs', () => {
+  // prettier-ignore
+  const str = 'Array' + printTree('', [
+    (tab) => '[5]: Object' + printTree(tab + ' '.repeat('[5]: '.length), [
+      (tab) => 'item 1',
+      (tab) => 'item 2',
+    ]),
+  ]);
+
+  expect('\n' + str).toBe(
+    `
+Array
+└─ [5]: Object
+        ├─ item 1
+        └─ item 2`);
+});
+

src/printTree.ts

@@ -1,15 +1,16 @@
 type Child = (tab: string) => string;
 
 export const printTree = (tab = '', children: (Child | null)[]): string => {
-  children = children.filter(Boolean);
   let str = '';
-  for (let i = 0; i < children.length; i++) {
-    const isLast = i >= children.length - 1;
+  const length = children.length;
+  const last = length - 1;
+  for (let i = 0; i < length; i++) {
     const fn = children[i];
     if (!fn) continue;
-    const child = fn(tab + `${isLast ? ' ' : '│'}  `);
-    const branch = child ? (isLast ? '└─' : '├─') : '│ ';
-    str += `\n${tab}${branch} ${child}`;
+    const isLast = i === last;
+    const child = fn(tab + (isLast ? ' ' : '│') + '  ');
+    const branch = child ? (isLast ? '└─' : '├─') : '│';
+    str += '\n' + tab + branch + (child ? ' ' + child : '');
   }
   return str;
 };

src/types.ts

@@ -1,6 +1,11 @@
+/**
+ * A resource that has `.toString()` with a tabbable output support. Which
+ * allows to chain the output of multiple objects in a tree-like structure.
+ */
 export interface Printable {
   /**
-   * Returns a human-readable tabbed string representation of the object as a tree.
+   * Returns a human-readable tabbed string representation of the object as a
+   * tree.
    *
    * @param tab String to use for indentation.
    */